Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS4797178 A
Publication typeGrant
Application numberUS 07/049,254
Publication dateJan 10, 1989
Filing dateMay 13, 1987
Priority dateMay 13, 1987
Fee statusLapsed
Also published asEP0298204A2, EP0298204A3
Publication number049254, 07049254, US 4797178 A, US 4797178A, US-A-4797178, US4797178 A, US4797178A
InventorsVu Q. Bui, Kevin K. Chan, Joseph G. Hoffarth, Vicki J. Malueg
Original AssigneeInternational Business Machines Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Carbon tetrafluoride and oxygen as a process gas
US 4797178 A
Abstract
The present invention provides a process for plasma cleaning and an improved gas mixture for use in a plasma cleaning process. The gas mixture of the present invention includes the normal process gases such as oxygen and carbon tetrafluoride. However, the mixture also includes a small percentage of a large mass inert gas such as Argon or Krypton. This large mass gas molecule mechanically removes any polymerized fluorocarbon that forms on the surface being cleaned thereby significantly enhancing the rate of etch or cleaning.
It has been found that five to twenty percent of the inert gas is the preferred range and that ten percent produces optimum results.
Images(4)
Previous page
Next page
Claims(9)
I claim:
1. A gas mixture for plasma cleaning comprising
a process gas including carbon tetrafluoride and oxygen in the ratio of about 60/40,
a large mass inert gas in the amount of about five to twenty percent by volume,
whereby the action of said process gas is not inhibited by any polymerized fluorocarbons that form on said surface.
2. The gas recited in claim 1 wherein said large mass inert gas comprises the class that includes Argon and Krypton.
3. A method of plasma cleaning a surface comprising,
subjecting said surface to a plasma process gas which includes carbon tetrafluoride and oxygen,
whereby non-polymerized organics are removed and polymerized fluorocarbons are formed on said surface,
simultaneously subjecting said surface to bombardment by a large mass inert gas, whereby said polymerized fluorocarbons are removed,
thereby enhancing the action of process gas.
4. The method recited in claim 3 wherein said large mass inert gas comprises the class that includes Argon and Krypton.
5. The method of plasma cleaning a surface comprising,
subjecting said surface to a plasma process gas which removes non polymerized organics from said surface,
simultaneously subjecting said surface to bombardment by a large mass inert gas, in sufficient amount to remove polymerized fluorocarbons without carbonizing said surface,
whereby the action of said process gas is enhanced by the action of said large mass inert gas.
6. The method recited in claim 5 wherein said large mass inert gas comprises the class that includes Argon and Krypton.
7. The method recited in claim 5 wherein said process gas includes oxygen and carbon tetrafluoride.
8. The method recited in claim 5 wherein said surface includes a printed circuit board.
9. A gas mixture for plasma cleaning comprising
a process gas including carbon tetrafluoride and oxygen,
a large mass inert gas in the amount of about ten percent by volume,
whereby the action of said process gas is not inhibited by any polymerized fluorocarbons that form on said surface.
Description
TECHNICAL FIELD

The present invention relates to the manufacture of printed circuit boards and more particularly to the removal of organic material from printed circuit boards using plasma gas.

BACKGROUND AND PRIOR ART The use of plasma gas to etch material is well known. For example, see U.S. Pat. Nos. 4,028,155, 4,545,851, 4,370,195, 4,370,196 4,536,271, 4,357,203 4,314,875 and 4,426,246.

It is also well known that during the manufacture of printed circuit boards, organic material can be removed from drilled holes and from the surface of a printed circuit board using plasma gas techniques. Normally in such plasma processes a mixture of oxygen and carbon tetrafluoride is used as the process gas. It is known that the etch rate in such plasma systems depend on a variety of parameters such as the amount of RF power, the chamber pressure, the feed gas flow rate, the feed gas composition, etc.

It is also known that the etch rate of organic polymers, photoresists and semi-conductor materials can be increased by alternating pure oxygen plasma with a CF4/O2 mixture (disclosure EN8850106, application serial number 718,246, filed Apr. 1, 1985, abandoned). Furthermore, it has been found that fast etching can be achieved by using several pulses of pure oxygen gas in conjunction with a CF4/O2 plasma (see RESEARCH DISCLOSURE, October 1986, Number 270, page 27025).

One factor which inhibits the efficacy of plasma clean operations is that during the cleaning operation, a monolayer of polymerized fluorocarbon sometimes forms on the surface of the material being cleaned. This layer of polymerized fluorocarbon has teflon like properties and it inhibits further cleaning by the plasma.

Other prior art techniques (such as that shown in U.S. Pat. No. 4,522,681) use a carrier gas along with the process gases. The process gases are gases such as oxygen and carbon tetrafluoride. The carrier gases are inert gases such as Helium and Argon. In such prior art the percentage of inert gas used is relatively high; that is, the percentage of inert gas is generally above thirty percent. Furthermore, since the inert gas is only used as a carrier, either a low mass gas such as Helium or a high mass gas such as Argon can be used.

OBJECTS OF THE INVENTION

An object of the present invention is to provide an improved process for cleaning printed circuit boards.

Another object is to provide an improved process for etching an organic material.

Yet another object of the present invention is to provide a plasma cleaning system which removes any polymerized fluorocarbon on the surface of the material being cleaned.

Another object of the present invention is to provide a plasma cleaning operation which removes any material which interferes with the adhesion of later applied catalyst or seeders.

Still another object of the present invention is to provide an improved mixture of fluorine containing gases for use in a plasma cleaning operation.

A still further object of the present invention is to provide an optimum mixture of gases for use in a plasma clean operation.

SUMMARY OF THE INVENTION

The present invention provides a process for plasma cleaning and an improved gas mixture for use in a plasma cleaning process. The gas mixture of the present invention includes the normal process gases such as oxygen and carbon tetrafluoride. However, the mixture also includes a small percentage of a large mass inert gas such as Argon or Krypton. This large mass gas molecule mechanically removes any polymerized fluorocarbon that forms on the surface being cleaned thereby significantly enhancing the rate of etch or cleaning.

It has been found that five to twenty percent of the inert gas is the preferred range and that ten percent produces optimum results.

DETAILED DESCRIPTION

The plasma etch process of the present invention can be practiced in commercially available parallel plate reactors such as those marketed by Branson Corporation and Advanced Plasma Systems Inc.

In practicing the present invention, the specimens to be etched or cleaned are placed on racks between the electrodes. The gas mixture of the invention is introduced into the reactor and RF power is applied to the plates of the reactor. A power density of about 0.1 to 1.0 (watts per square centimeter) of electrode area is used. The RF frequency can be in the range of about 15 kilohertz to 13.5 megahertz.

The material being etched or cleaned is subjected to the plasma for about 20 to 30 minutes at a power of about 3000 to 4000 watts and a gas flow rate of about 2000 to 3000 standard cubic centimeters per minute (sccm). In a reactor such as the one manufactured by Advanced Plasma Systems which has two gas inlets, a cycle time between inlets of one minute is used.

It has been found that by including about five to twenty percent (on a volume basis) of an inert gas having a large mass such as Argon or Krypton, the etch rate is significantly increased. The reason for this is that the large molecules of the inert gas will in effect physically remove any polymerized fluorocarbon that forms on the surface that is being etched or cleaned. It is believed that the large mass inert gas influences the surface chemistry and resultant etch rate due to the sputtering effect of the large mass inert gas ions. Thus, for a given polymer, the optimum etch rate occurs when the sputtered ions reduce the surface fluorination but do not result in carbonation of the polymer surface. It is noted that a normal plasma such as CF4/O2 does not attack or affect a polymerized fluorocarbon surface. While use of about five to twenty percent of a large mass inert gas is the preferred range, optimum performance can be obtained by using about ten percent by volume of the inert gas. While Argon and Krypton are the preferred large mass gases, it is noted that Argon is less expensive and that other large mass gases could be used.

The following specific examples further illustrate the invention, it being understood that the invention is in no way intended to be limited to the details in these examples. Each of these examples was done in a commercially available parallel plate reactor of the type marketed by Advanced Plasma System, model number 2400:

EXAMPLE 1

Pressure 300 microns

Power 4000 watts

Flow rate 3000sccm

Gas cycle 1 minute

Process Time 20 minutes

CF4/ O2 ratio 60/40

EXAMPLE 1a

______________________________________Argon Concentration          Weight Loss______________________________________0 percent      0.62E-4 grams per square cm.______________________________________
EXAMPLE 1b

______________________________________Argon Concentration          Weight Loss______________________________________5 percent      0.84E-4 grams per square cm.______________________________________
EXAMPLE 1c

______________________________________Argon Concentration          Weight Loss______________________________________10 percent     1.17E-4 grams per square cm.______________________________________
EXAMPLE 1d

______________________________________Argon Concentration          Weight Loss______________________________________15 percent     1.10E-4 grams per square cm.______________________________________
EXAMPLE 1e

______________________________________Argon Concentration          Weight Loss______________________________________20 percent     1.02E-4 grams per square cm.______________________________________
EXAMPLE 2

Pressure 300 microns

Power 4000 watts

Flow rate 3000 sccm

Gas cycle 1 minute

Process Time 30 minutes

CF4/ O2 ratio 60/40

EXAMPLE 2a

______________________________________Argon Concentration          Weight Loss______________________________________0 percent      0.7E-4 grams per square cm.______________________________________
EXAMPLE 2b

______________________________________Argon Concentration          Weight Loss______________________________________5 percent      0.92E-4 grams per square cm.______________________________________
EXAMPLE 2c

______________________________________Argon Concentration          Weight Loss______________________________________10 percent     2.43E-4 grams per square cm.______________________________________
EXAMPLE 2d

______________________________________Argon Concentration          Weight Loss______________________________________15 percent     2.21E-4 grams per square cm.______________________________________
EXAMPLE 2e

______________________________________Argon Concentration          Weight Loss______________________________________20 percent     2.10E-4 grams per square cm.______________________________________
EXAMPLE 3

Pressure 300 microns

Power 4000 watts

Flow rate 2000 sccm

Gas cycle 1 minute

Process Time 30 minutes

CF4/ O2 ratio 60/40

EXAMPLE 3a

______________________________________Argon Concentration          Weight Loss______________________________________0 percent      0.57E-4 grams per square cm.______________________________________
EXAMPLE 3b

______________________________________Argon Concentration          Weight Loss______________________________________5 percent      0.79E-4 grams per square cm.______________________________________
EXAMPLE 3c

______________________________________Argon Concentration          Weight Loss______________________________________10 percent     1.27E-4 grams per square cm.______________________________________
EXAMPLE 3d

______________________________________Argon Concentration          Weight Loss______________________________________15 percent     1.10E-4 grams per square cm.______________________________________
EXAMPLE 3e

______________________________________Argon Concentration          Weiqht Loss______________________________________20 percent     1.04E-4 grams per square cm.______________________________________

While preferred embodiments of the invention have been described above, many modifications can be made thereto without departing from its spirit and scope. Accordingly, the invention is not limited by the foregoing description, but it is only limited by the scope of the appended claims.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4472238 *Dec 5, 1983Sep 18, 1984E. I. Du Pont De Nemours And CompanyProcess using plasma for forming conductive through-holes through a dielectric layer
US4601782 *Jun 20, 1985Jul 22, 1986International Business Machines Corp.Reactive ion etching process
US4654115 *Apr 8, 1986Mar 31, 1987International Business Machines CorporationProcess for removing contaminant
US4689111 *Oct 28, 1986Aug 25, 1987International Business Machines Corp.Impinging slurry containing suspended metal oxide, exposing to fluorohydrocarbon plasma gas
US4720322 *Apr 13, 1987Jan 19, 1988Texas Instruments IncorporatedPlasma etching of blind vias in printed wiring board dielectric
Non-Patent Citations
Reference
1"Optical Emission Spectroscopy of Reactive Plasmas: A Method of Correlating Emission Intensities to Reactive Particle Densities", J. W. Coburn et al, J. Appl. Phys. 51 (6), Jul. 1980.
2 *Optical Emission Spectroscopy of Reactive Plasmas: A Method of Correlating Emission Intensities to Reactive Particle Densities , J. W. Coburn et al, J. Appl. Phys. 51 (6), Jul. 1980.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5108542 *Aug 23, 1990Apr 28, 1992Hewlett Packard CompanySelective etching method for tungsten and tungsten alloys
US5129958 *May 23, 1991Jul 14, 1992Applied Materials, Inc.Cleaning method for semiconductor wafer processing apparatus
US5163458 *May 22, 1991Nov 17, 1992Optek, Inc.Method for removing contaminants by maintaining the plasma in abnormal glow state
US5176791 *Jul 15, 1991Jan 5, 1993Semiconductor Energy Laboratory Co., Ltd.Method for forming carbonaceous films
US5294572 *Mar 6, 1990Mar 15, 1994Asm International N.V.Method and apparatus for depositing a layer on a substrate
US5316591 *Aug 10, 1992May 31, 1994Hughes Aircraft CompanyCleaning with liquid carbon dioxide, nitrous oxide, sulfur hexafluoride or xenon plastic substrates
US5451263 *Feb 3, 1994Sep 19, 1995Harris CorporationMarking integrated circuits with metal parts and adhesion of inks
US5700327 *Mar 10, 1995Dec 23, 1997Polar Materials, IncorporatedMethod for cleaning hollow articles with plasma
US5817578 *May 16, 1996Oct 6, 1998Nec CorporationMethod of cleaning vacuum processing apparatus
US5824375 *Oct 24, 1996Oct 20, 1998Applied Materials, Inc.Reducing sorbable contaminants in a reactor using a cleaning gas; integrated circuits, semiconductors
US5833758 *Nov 20, 1996Nov 10, 1998Harris CorporationExposing metal coated backside surface to argon plasma removes carbonates, oxides, and surface contaminants, then exposing to hydrogen plasma chemically reduces and passivates metal; efficiency, nondeforming
US5882423 *Nov 20, 1996Mar 16, 1999Harris CorporationGas phase plasma cleaning method is utilized for removing contaminants from the surface of exposed metallic, ceramic and plastic parts on integrated circuit, using a gas mixutre of argon and oxygen
US6092714 *Mar 16, 1999Jul 25, 2000Mcms, Inc.Method of utilizing a plasma gas mixture containing argon and CF4 to clean and coat a conductor
US6255179Aug 4, 1999Jul 3, 2001International Business Machines CorporationPlasma etch pre-silicide clean
US6449521Sep 18, 1998Sep 10, 2002Applied Materials, Inc.Decontamination of a plasma reactor using a plasma after a chamber clean
US6461974Oct 6, 2000Oct 8, 2002Lam Research CorporationHigh temperature tungsten etching process
US6686296Nov 28, 2000Feb 3, 2004International Business Machines Corp.Nitrogen-based highly polymerizing plasma process for etching of organic materials in semiconductor manufacturing
US7578944 *Nov 14, 2005Aug 25, 2009Samsung Electronics Co., Ltd.Apparatus for generating gas plasma, gas composition for generating plasma and method for manufacturing semiconductor device using the same
US8083892Mar 13, 2009Dec 27, 2011Samsung Electronics Co., Ltd.Apparatus for generating gas plasma, gas composition for generating plasma and method for manufacturing semiconductor device using the same
WO1995002472A1 *Jul 12, 1994Jan 26, 1995Fusion Systems CorpPost treatment of a coated substrate with a gas containing excited halogen to remove residues
WO2000077792A1 *Jun 15, 1999Dec 21, 2000Kim Yong SooAn effective dry etching process of actinide oxides and their mixed oxides in cf4/o2/n2 plasma
Classifications
U.S. Classification134/1.1, 252/79.1, 216/58, 204/192.36, 216/67, 134/1
International ClassificationH01L21/302, H05K3/08, C23F4/00, H05K3/00, B08B7/00, H01L21/3065, C23G5/00, H05K3/26
Cooperative ClassificationH05K2203/095, H05K3/0055, B08B7/0035, C23G5/00
European ClassificationH05K3/00K6, B08B7/00S, C23G5/00
Legal Events
DateCodeEventDescription
Mar 25, 1997FPExpired due to failure to pay maintenance fee
Effective date: 19970115
Jan 12, 1997LAPSLapse for failure to pay maintenance fees
Aug 20, 1996REMIMaintenance fee reminder mailed
May 13, 1992FPAYFee payment
Year of fee payment: 4
Jul 10, 1987ASAssignment
Owner name: INTERNATIONAL BUSINESS MACHINES CORPORATION, ARMON
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:BUI, VU Q.;CHAN, KEVIN K.;HOFFARTH, JOSEPH G.;AND OTHERS;REEL/FRAME:004796/0059;SIGNING DATES FROM 19870508 TO 19870514
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BUI, VU Q.;CHAN, KEVIN K.;HOFFARTH, JOSEPH G.;AND OTHERS;SIGNING DATES FROM 19870508 TO 19870514;REEL/FRAME:004796/0059